In semiconductor packaging, mold compounds are normally used to encapsulate flip-chip dies and or wire-bonding dies to protect the dies against damage from the outside environment. Further, the mold compounds are also used to underfill the flip-chip dies to provide mechanical support to interconnects of the flip-chip dies. However, direct contact of the mold compounds and active die surfaces may adversely impact the electrical performance of the dies, especially for dies that support high frequency applications. Accordingly, it is desirable to package the dies in a configuration for better high frequency performance.
With developed semiconductor fabrication technology and popularity of portable communication electronic devices, such as cellular phones, tablet computers, and so forth, high levels of integration of semiconductor packages are highly desired. Package on package (POP), which stacks two or more semiconductor packages vertically, is a semiconductor packaging technology that allows higher electronics density in final products. POP benefits small printed-circuit-board areas and short trace lengths between different semiconductor packages. However, for applications that have thickness limitations, POP may not meet the thickness or performance requirement.
Accordingly, there remains a need for improved package designs to increase the integration level of semiconductor packages and enhance the high frequency performance of the semiconductor packages without significantly increasing the package size. In addition, there is also a need to keep the final product cost effective.